1. Field of the Invention
The invention relates to fluid flowmeters and in particular to flowmeters of the vortex shedding type in which the vortices are detected optically.
2. Description of the Prior Art
In flowmeters of the vortex shedding type a so-called bluff body is placed in the fluid stream and sheds vortices into the fluid at a frequency which is a function of the fluid flow velocity. Thus by detecting these vortices and measuring the rate at which they are generated the flow velocity of the fluid can be determined.
The phenomenon of changing index of refraction in a fluid medium as a function of fluid density is known and has been exploited for density measurement. The instrumentations of the prior art and their purposes are varied, typical examples being shown in British Pat. Nos. 981,753; 1,362,732; and 1,514,977. A flowmeter instrumentation employing a vortex shedding bluff body in a fluid flow for creating vortices is described in British Pat. No. 1,544,636. The detection of passing vortices is effected through changes in light attennation in an unclad optical fiber in the fluid flow downstream from the bluff body. Although that arrangement is workable, it will be seen that the invention provides a more sensitive vortex detector of more rugged structure. The details of construction and operation of a typical embodiment according to the invention will be understood from the description following.